Various information processing systems have been developed as a result of the rapid development which has taken place in the information industry in recent years. Methods of recording and apparatus compatible with these information processing systems have been developed and adopted. Thermal transfer recording methods, i.e., recording methods of this type, involve the use of an apparatus which is light and compact, with which there is little noise, and which has excellent operability and maintenance characteristics. Moreover, since they also allow coloring to be achieved easily, these methods are the most widely used. Thermal transfer recording methods can be broadly classified into two types, namely, thermofusion types and thermomobile types. In the latter case, a thermal transfer dye providing material which has, on a support, a dye providing layer which contains a binder and a thermomobile dye is laminated with a thermal transfer image receiving material, heat is applied from the support side of the dye providing material, the thermomobile dye is transferred to the recording medium (thermal transfer image receiving material) in the form of a pattern corresponding to the heat pattern which has been applied and an image is formed.
Moreover, a thermomobile dye is, for example, a dye which can be transferred from a thermal transfer dye providing material to a thermal transfer image receiving material by sublimation or diffusion in a medium.
However, the following disadvantages are encountered with thermal transfer image receiving materials in which the thermomobile type thermal transfer recording method is employed.
The polymers used in the receiving layer for the thermomobile dye are soluble in organic solvents and so an organic solvent system is used for the receiving layer coating liquid. Furthermore, the apparatus and vessels used , in the manufacturing process must be cleaned with organic solvents. Hence, the apparatus used for preparing the coating liquid and the coating apparatus must be explosion-proof. Furthermore, organic solvents are very expensive when compared to water and so the production costs are increased. Moreover, problems can arise with the health supervision of the operators. As stated above, conventional thermal transfer image materials using organic solvents have various problems with regard to the adoptability for the production thereof.
Various attempts have been made to obtain an image having a high transfer density in the thermomobile type thermal transfer image receiving method.
For example, JP-A-60-38192 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses the use of latexes of dye accepting polymers as coating solutions for the image receiving layer. However, the resulting image is not considered to be satisfying with respect to transfer density, because the transfer density is low. Further, when the thermal transfer image receiving material is placed on the thermal transfer dye providing material and heat is applied thereto to transfer the thermomobile dye from the dye providing material to the image receiving material in the method described in the above patent specification, problems are often caused in that both materials are fused together by heat, and the dye providing layer of the dye providing material is peeled off and stuck on the transfer surface of the image receiving material, or conveying is sometimes made impossible and the printer is stopped. These troubles are caused particularly when the applied voltage is raised and thermal transfer is carried out at high temperatures to obtain a sufficient transfer density. Further, when additives are used to increase the transfer density of the thermal transfer image receiving material or to prevent heat fusion from being caused, it has been found that the image quality of the image receiving material is liable to be deteriorated.
JP-A-57-137191, JP-A-57-91296 and JP-A-60-38192 disclose that the dispersions of the latexes of dye accepting polymers in polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) or hydroxyethyl cellulose (HEC) are used as coating solutions for the image receiving layer to improve image density. It has been found that an effect of improving image density is somewhat obtained. However, the effect is low and insufficient.
The present inventors have made studies to solve the above-described problems caused when the organic solvent solutions of the dye accepting materials are coated.